This invention relates to processes for the preparation of aromatic substances from diterpene fractions. More particularly, the invention provides a novel process for preparing aromatic substances from diterpene fractions in an environment free of photochemically active radiation.
The surface resin of fresh tobacco plants contain diterpenes which, being smoke aroma precursors, influence the aroma of tabacco. Diterpene fractions are obtainable from many sources. For example, they can be obtained by extraction from the surface resin of fresh tobacco plants or parts of these, by extraction from raw tobacco or tobacco waste, e.g., tobacco dust, or by extraction from the plant gum derived from the tobacco blossoms. They can also be prepared synthetically.
A number of processes for isolating diterpenes from the surface resin of tobacco plants are known. In these processes undesired lipids present in the resin are removed. An example of this process is disclosed in German Offenlengungsschrift No. 2,918,920.
Photochemical reactions involving diterpenes are well known. The smoke aroma precursor properties of diterpenes isolated from tobacco plants has prompted work regarding the chemical structure of diterpenes and their reactions. In particular, diterpene photoreactions with singlet oxygen has been studied. For example, Acta Chemica Scandinavia 1979, pages 437-442 discloses such work. In these investigations, photo-oxidation of diterpenes was carried out in the presence of photochemical catalysts (sensitisers), for example Bengal Rose.
Various processes for preparing aromatic substances through photochemical reactions are known. German Patent Specification No. 3,009,032 and its counterpart U.S. Pat. No. 4,359,059 disclose a process for the preparation of aromatic substances by UV radiation of a tobacco extract containing diterpenes. The extract is irradiated in the presence of oxygen in the absence of photochemical catalysts (sensitisers). The oxidation is thus carried out by a conventional free-radical mechanism.
In another process, aromatic substances are prepared from a carotenoid fraction obtained from tobacco plants in which any diterpenes have been removed. The carotenoid fraction is oxidized with oxygen, in alcoholic solution, and with UV radiation. This process is disclosed, for example, by German Patent Specification No. 3,009,031 and its counterpart U.S. Pat. No. 4,351,346. The process can be carried out in the presence of photochemical catalysts (sensitisers) or in the absence of these. The reaction takes place either by means of a free-radical mechanism or via singlet oxygen as the oxidizing agent.
The present inventors have discovered a process for preparing tobacco aromatic substances that does not employ a photo-oxidation reaction. The resulting aromas have aromatic properties superior to those of the substances obtained by photochemical processes. Aromatic as used herein refers to odor and is not to be interpreted as reference to benzene or benzene type compounds.